The same reading without the calendar: count back from TODAY over the last 20 daily candles, and again over the last 3. Both windows move forward with every new day.
Why rolling — The monthly-anchored 20/40/60 stays put for a whole month. These two are recounted from today, so they track what price has just done.
3 days — The shortest window, and usually the one an intraday reaction is actually respecting.
Read them together — Discount of the 20-day window while sitting in premium of the 3-day one is a very different picture from both agreeing.